1. Field of the Invention
The present invention relates to a silver halide photographic material, in particular to one which has improved antistatic and antiblocking properties and which is free from the problem of unevenness in image density due to the fouling of transport rollers.
2. Description of the Prior Art
The outermost layer of silver halide photographic materials generally uses hydrophilic colloids (typically gelatin) as binders. Because of the use of such binders, the surface of silver halide photographic materials, when placed in a hot and humid atmosphere, will have increased adhesiveness or stickiness and will readily stick to other objects with which they come in contact.
This phenomenon commonly referred to as "blocking" in the art will take place between two adjacent silver halide photographic materials or between a silver halide photographic material and another object with which it comes in contact during manufacture or storage of the silver halide photographic materials or during imaging (i.e., when pictures are taken on such photographic materials). The blocking phenomenon has been a great concern in the art, particularly in silver halide color photographic materials which incorporate color couplers and many other additives in photographic layers.
In order to solve this problem, it has been proposed that the blocking nature of silver halide photographic materials be decreased by incorporating the fine particles of inorganic substances (e.g., silicon dioxide, magnesium oxide, titanium dioxide and calcium carbonate) or organic substances (e.g., polymethyl methacrylate, cellulose acetate propionate and fluoropolymers) so that the photographic materials will have a roughened (i.e., matted) surface. For the reason already mentioned, such matting agents have to be incorporated in large quantities in silver halide color photographic materials. However, if matting agents are used in excessive amounts, image quality, in particular, sharpness of image is adversely affected. Therefore, there is a certain limit on the amount of matting agents that can be employed.
Besides the blocking phenomenon, buildup of static charges is another great concern in silver halide photographic materials which usually employ electrically insulating supports. While static buildup can cause many troubles, the most serious one is that the static electricity that has built up before processing is discharged to allow the lightsensitive emulsion layer to become exposed so that unevenness in image density either in the form of circular spots or tree-like or feather-like marks will occur in the processed films. These spots or marks are generally referred to as "static marks" in the art and greatly impair the commercial value of photographic films. For instance, static marks on the surface of a developed medical or industrial X-ray film can mislead the doctor to a wrong and, hence, very dangerous diagnosis. One of the problems associated with static marks is that they become evident only after development has been undertaken. Static buildup can induce secondary troubles such as attraction of dust particles to the film surface and failure to form a uniform coating layer.
As already mentioned, buildup of static charges often occurs during manufacture and use of photographic materials. In the manufacturing process, the frictional contact between a photographic film and rollers, or the separation between the surfaces of the support and the emulsion layer that takes place during film winding or rewinding is the primary cause of static buildup. Static charges will also develop in a finished photographic film roll when the base surface of a layer separates from the emulsion surface of an adjacent layer as the film is wound up in a camera. In X-ray films, static buildup occurs as a result of contact with, and separation from, a fluorescent intensifying screen or the mechanical parts of the automatic film imaging apparatus. Static buildup also occurs in finished photographic films when they come in contact with packaging materials. The severity of static marks that are induced in photographic materials as a result of static buildup increases as the sensitivity of the photographic materials or the rate of development and subsequent steps of photographic processing increases. Modern photographic materials are designed to have higher sensitivities and the chance of their being subjected to handling under hostile conditions is increasing because of the requirement for employing higher speeds on such occasions as application of coating layers, imaging, and automatic processing. These factors all lead to an even greater chance of the occurrence of static marks.
In order to avoid the occurrence of troubles due to 15 static electricity, it is preferable to incorporate antistatic agents in photographic materials. However, not all of the antistats that are in common use can be straight forwardly employed in photographic materials because the use and choice of suitable antistats is subject to various constraints that are peculiar to photographic materials. Antistatic agents that can be used in photographic materials must of course exhibit a good antistatic performance. In addition, they must satisfy various other requirements such as freedom from any adverse effects on the film quality and antiblocking properties of the photographic material in which they are incorporated, freedom from the chance of causing premature contamination of processing solutions, and freedom from unevenness in the density of image formed on the film that may occur after processing as a result of the fouling of transport rollers. In this way, the application of antistats to photographic materials is limited by a large number of factors.
With a view to providing enhanced electrical conductivity for the support and coated surface layers of silver halide photographic materials, the use of various kinds of hydroscopic substances, water-soluble inorganic salts, surfactants and polymers has been attempted. For example, the use of surfactants is described in U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, and Japanese Patent Application (OPI) Nos. 7762/1980, 3636/1981 and 114944/1981 (the term "OPI" as used hereinafter means an unexamined published Japanese patent application), and the incorporation of polymers is shown in U.S. Pat. Nos. 2,882,157, 3,062,785, 3,938,999, and Japanese Patent Application (OPI) Nos. 78834/1981, 204540/1982, 179837/1982 and 2242/1983.
However, it is very difficult to accomplish complete prevention of static buildup on hydrophilic colloidal layers and known antistatic methods either fail to cause a satisfactory drop in surface resistivity at low humidities or sometimes induce "blocking" problems in a hot and humid atmosphere. In addition, if an antistat (e.g., a fluorine-containing surfactant of the type described in Japanese Patent Publication No. 44411/1981) is incorporated in a hydrophilic colloidal layer in the necessary amount to attain the intended antistatic effect, the quality of that layer may be adversely affected or the antistat will be transferred into processing solutions so as to cause unwanted phenomena such as sludge formation.
The use of an antistatic agent in the form of a nonionic surfactant containing a polyoxyethylene unit is disclosed in such prior patents as Japanese Patent Application (OPI) No. 80023/1977, West German Patent Nos. 1,422,809 and 1,422,818, and Australian Patent No. 54,441/1959. The nonionic surfactants with a polyoxyethylene unit that are shown in these patents impart improved antistatic properties to the photographic materials in which they are incorporated but, on the other hand, they cause adverse effects on the photographic characteristics of the product such as the sensitivity, antifogging property, granularity and sharpness of photographic emulsions; in addition, such nonionic surfactants will contaminate processing solutions or product unwanted deposit formation on rollers.
According to Japanese Patent Publication No. 9610/1986, the antistatic performance of an ethylene oxide addition polymer of the condensation product of phenol and formaldehyde can be improved by combining it with a variety of coating aids. However, this method is incapable of preventing the occurrence of troubles due to the fouling of transport rollers or contamination introduced in the stage of photographic processing.
Japanese Patent Application (OPI) Nos. 29715/1978 and 76741/1985 disclose photographic materials containing a specified anionic surfactant and a nonionic surfactant having a polyoxyethylene unit. These methods, however, are still ineffective for the purpose of preventing the occurrence of film troubles due to the contamination of processing solutions or the fouling of transport rollers.
Japanese Patent Application (OPI) Nos. 76742/1985 and 80849/1985 disclose techniques that rely on the combined use of a fluorine-containing compound with a nonionic surfactant having a polyoxyethylene unit. These methods provide an improved antistatic performance but they still are incapable of solving the aforementioned problems occurring in the processing stage, namely, the contamination of processing solutions and the fouling of transport rollers, both of which will lead to the unevenness of image density attainable by photographic processing.